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Effects of dietary fibre type on blood pressure: A systematic review and
meta-analysis of randomised controlled trials of healthy individuals
Short title: fibre and blood pressure
By Charlotte E.L. EVANSa, Darren C. GREENWOODb , Diane E. THREAPLETONa, Christine
L. CLEGHORNa, Camilla NYKJAERa, Charlotte E. WOODHEADa, Christopher P. GALEb and
Victoria J. BURLEYa
aNutritional Epidemiology Group, School of Food Science and Nutrition, University of Leeds,
LS2 9JT, UK
bCentre for Epidemiology & Biostatistics, Level 8 Worsley Building, University of Leeds, LS2
9JT, UK
Charlotte E.L. Evans Lecturer in Nutritional Epidemiology, Diane E. Threapleton Doctoral
Student, Christine L. Cleghorn Research Fellow, Camilla Nykjaer Research Assistant, Charlotte
E. Woodhead Research Assistant, Darren C. Greenwood Senior Lecturer in Biostatistics, Chris
P. Gale Associate Professor in Cardiovascular Health Sciences and Honorary Consultant
Cardiologist, Victoria J. Burley Associate Professor in Nutritional Epidemiology
Conflicts of interest and Source of funding:
No conflicts of interested were declared by any of the authors. The large systematic review of
carbohydrates and cardio-metabolic health was funded by the Department of Health for
England.
Corresponding author: Charlotte E.L. Evans
Email: [email protected]
Telephone: 0113 343 3956
Fax: 0113 343 29821
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No reprints will be made available
Word count:
Number of tables: 3
Number of figures: 5
Number of supplementary files: 4
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Abstract
Objective To determine the effect of different types of dietary fibre on systolic and diastolic
blood pressure.
Methods: A systematic review of the literature and a meta-analysis of randomised controlled
trials using random effects models. Eligibility criteria for studies included randomised
controlled trials of at least 6 weeks duration testing a fibre isolate or fibre rich diet against a
control or placebo published between 1st January 1990 and 1st December 2013.
Results 28 trials met the inclusion criteria and reported fibre intake and systolic blood pressure
(SBP) and/or diastolic blood pressure (DBP). 18 trials were included in a meta-analysis. Studies
were categorised into one of twelve fibre-type categories. The pooled estimate for all fibre types
were -0.9 mmHg (95% CI -2.5 to 0.6 mmHg), and -0.7 mmHg (95% CI -1.9 to 0.5 mmHg) for
SBP and DBP respectively. Analyses of specific fibre types concluded that diets rich in beta-
glucans reduce SBP by 2.9 mmHg (95% CI 0.9 to 4.9 mmHg) and DBP by 1.5 mmHg (95% CI
0.2 to 2.7 mmHg) for a median fibre difference of 13 g. Heterogeneity for individual fibre types
was generally low.
Conclusions Higher consumption of beta-glucan fibre found in oats and barley is associated
with lower systolic and diastolic blood pressure; however evidence for other types of fibre was
not consistent. In many countries total dietary fibre consumption is considerably lower than
recommended. Policies which increase oat and barley consumption and reduce cardiovascular
disease, through lowering blood pressure, should be encouraged.
Keywords:
Blood pressure; fibre; beta-glucans; CVD risk; systematic review; meta-analysis
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Introduction
A third of all deaths in the UK are attributed to diseases of the heart and circulatory system.[1]
Hypertension or high blood pressure is a major risk factor for stroke and myocardial
infarction[2] and is also a common cause of kidney disease. Hypertension, therefore, contributes
significantly to morbidity and mortality rates.[3] [4] It is suggested that hypertension affects up
to one quarter of the population worldwide [5] although in Western Countries up to half of the
adult population are reported to have blood pressure levels outside the desirable range.[6]
International guidelines recommend diagnostic and treatment thresholds for hypertension.[7, 8]
In addition to prescribed medications, the management of hypertension involves lifestyle
changes. These include the maintenance of a healthy weight, stopping smoking, reducing
alcohol consumption, and dietary changes such as a low salt diet rich in fruit and vegetables.[9]
The average individual effect size noted in dietary intervention trials is generally relatively
small. For example, Neter et al. suggested that for every 1 kg weight loss, systolic and diastolic
blood pressure would decrease by 1 mmHg.[10] However, these small effects, can translate into
important reductions in the incidence of hypertension at thea population level.[11] It is
estimated that each 2mmHg reduction in systolic blood pressure and 1mmHg reduction in
diastolic blood pressure is associated with a 10% reduction in the risk of CVD.[12]
Although advice on increasing fruit and vegetable consumption is included in guidance to
reduce blood pressure, advice on fibre consumption is not. Two reviews of fibre and blood
pressure were published in 2005. Although they described a significant inverse relationship
between fibre consumption and blood pressure, they did not describe the effects by fibre type.
[13] [14] Since the publication of these reviews many more studies have been conducted
exploring different fibre isolates and it is now timely to determine the effect of different types of
fibre on blood pressure. A high fibre diet, particularly if higher in soluble fibre, is associated
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with additional health outcomes; including better glucose control and lipid profile[15-17] but
less data is available on different types of fibre and their importance on blood pressure.
This review categorises fibre into twelve groups based on their chemical structure, as
recommended by Wanders et al.[18] Nine categories of fibre are isolated fibres and three are
complex mixtures of fibre rich diets. The aim of this review is therefore to determine the effects
of specific types of dietary fibre on systolic and diastolic blood pressure in a healthy population.
Methods
Selection of trials
This review is part of a large review of carbohydrates and cardio-metabolic disease which
followed PRISMA (Preferred Reporting Items for Systematic Reviews and Meta-Analyses)
guidelines.[19] Human studies published in English since 1990 until December 2009 were
included in the original review and the search was updated to include studies up to 1st December
2013. The following electronic databases were searched in the original review: Medline, Pre-
Medline (MEDLINE in process), Embase, CAB Abstracts, BIOSIS, ISI Web of Science and The
Cochrane Library. The update search included Medline and Embase databases only. Electronic
searches were supplemented with hand searches in key journals and citation lists of selected
review articles. Search terms included MeSH terms for different types of fibre namely “fiber”,
“fibre”, “fibre isolate”, “beta-glucans”, and “wholegrain” as well as the MeSH term for blood
pressure. The BMJ search strategy for trials was used.[20] The protocol was agreed by all
research personnel prior to starting the review and peer-reviewed by panel members of the
Scientific Advisory Committee on Nutrition (SACN) carbohydrate working group and
Department of Health (DoH) personnel and is published on their website in a draft report.[21]
Inclusion criteria were applied which included were parallel or crossover randomised controlled
trials (RCTs) of at least 6 weeks duration where they reported a difference in fibre intake
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between an intervention group and a comparator group and measured blood pressure at baseline
and at least one other time point. There were no age or gender restrictions. Studies were
excluded if ill health or history of disease was part of the inclusion criteria for the study.
Specifically, studies in which >10% of the population were diagnosed with hypertension were
excluded. Outcomes in the full review included markers of CVD such as blood pressure, blood
lipids as well as markers of inflammation and markers of vascular function. Many outcomes
that were included in the original search criteria are not reported here.
Studies were categorised into one of twelve possible groups including three for complex fibres
and nine categories of isolated fibres. The first group includes arabinoxylan, beta-glucan and
pectin rich diets. The second group includes glucans, resistant starch, dextrins, mannans,
fructans, xylans, pectins, marine polysaccharides and chitosan. Arabinoxylan rich diets include
trials where whole grain versions of foods are included which do not increase levels of other
macronutrients in the diet such as protein. High fibre diets that solely increased fruit and
vegetable intake were excluded as these foods contain a range of compounds in addition to fibre
that may potentially affect blood pressure such as flavanols. Protein rich high fibre foods such as
beans and legumes were also excluded as these foods would be likely to result in a change in the
macro-nutrient profile of participants.
Data screening and extraction
For each reference, the title and/or abstract were screened for article relevancy using the agreed
guidelines established at the start of the review. Letters and editorials were marked as ‘not
relevant’ as were all references clearly unrelated to the scope of the review. All other articles
were marked as ‘potentially relevant’ and were reviewed independently by two members of the
review team using an agreed Inclusion/Exclusion form. Where any disagreement occurred, a
third member of the team arbitrated in the decision.
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Data on exposures, outcomes, sample size, participants, study-design and length of intervention,
were entered directly into an access database. Authors were not contacted, and only data
reported in tables (but not figures) were extracted. Data reported only in figures and not in tables
was not extracted and authors were not contacted. Data extraction was completed by one of
several members of the review team with serial review for extraction errors.
Quality assessment of trials
The review was not restricted on the basis of perceived quality of papers or the process of
obtaining data cited in primary studies. The quality of trials included in at least one meta-
analysis was assessed in duplicate using the Cochrane indicators of bias[22] and covered the
following issues: sequence generation criteria for random allocation, allocation concealment,
blinding of participants, blinding of personnel and outcome assessors, incomplete reporting of
outcome data, selective outcome reporting and other potential threats to validity. Each paper was
categorised as containing bias, no bias or being unclear based on each of the above criteria.
Statistical analysis
Data from all arms of the trial were extracted and the two arms with the largest difference in
fibre were included in the analysis. Results of the trial were included if data were provided in
one of the following two formats: a difference between the intervention and control group either
adjusted or unadjusted for baseline results or a change from baseline to follow up for each arm.
In the latter case the difference in the change between groups was calculated using a t-test to
provide the difference between groups with a measure of variation. Studies were excluded if
only a p value was provided for the difference between arms.
Where results from at least three included studies could be quantitatively combined for each
fibre type, a random effects meta-analysis of the intervention trial data was reported. A
weighted mean difference was calculated (weighted by the inverse of the variance). All the
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results of studies were expressed as the difference in systolic and diastolic blood pressure in
mmHg between study arms.
Heterogeneity was presented as the proportion of total variation in study estimates that is due to
between study heterogeneity (I2).[23] It is common to interpret I2 as being excessive where the
value is in excess of 50 to 75%; we chose to use 75% as our cut off.[24] Where values were
above this, a pooled estimate was reported but no conclusions were drawn. Small study effects
such as publication bias were assessed using a funnel plot for all trials combined and for a
specific fibre type if the number of studies exceeded ten. A broadly symmetrical funnel plot
was taken to indicate no evidence of small study effects. Meta-regression was carried out
onundertaken for factors potentially contributing to heterogeneity including gender, weight
status and dose response. Dose response was analysed for total fibre intake as well as by
individual fibre type for fibre categories with at least 3 results.
Results
Search results
Twenty eight trials were identified which met all the exclusion and inclusion criteria; 19 from
the original search and nine from the update search (see figure 1). The main reasons for
exclusion were; no blood pressure data reported, participants not healthy or not a relevant fibre.
Trial characteristics
The 28 trials were carried out in a number of different countries and therefore a range of
populations with different diets were represented (see Table 1); Nearly half of the studies were
conducted in the US (11 studies) and other countries included in the review were, Australia (3),
Denmark (2), Finland (2), Sweden (2) with one study each from Japan, Norway, Italy, New
Zealand, Germany, Israel, Netherlands and France. Most of the trials used a parallel group
design while five studies used a crossover design. The duration of the intervention ranged from
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six weeks to 14 months (see table 1). All except one study[25] included adults as participants,
with a mean age of between 29 and 60 years. Six studies included men only[25-30] and three
studies included women only.[31-33] Most trials were small and recruited between 21 and 172
participants in total with a mean of 62 participants.
Eighteen trials were included in at least one meta-analysis. Results from the remaining ten
studies were excluded for the following reasons; a lack of information on estimates of variation,
[29, 34-39] systolic and diastolic pressure not separately,[40] difference between groups was
based on molecular weight,[41] or data were only provided in a figure.[42]
The meta-analyses included a total of 1333 participants providing results for SBP and 1183
providing results for DBP. Although all the studies included generally healthy populations,
many studies included overweight or obese participants, often as part of the inclusion criteria
(see table 1). Body weight was usually reported to decrease in both arms of the trial with mean
weight loss in the control group reported as 1.6 kg and mean weight loss in the intervention
group reported as 1.8 kg. Twelve out of the eighteen studies included in the meta-analysis
reported differences in body weight change between arms ranging from 2.5 kg more weight loss
in the control group to 1.2 kg more weight loss in the intervention group. These differences
were generally modest (mean and median difference in weight loss between arms of 0.2 kg,) and
nine out of the twelve trials reported differences of less than 1 kg.
The interventions to increase fibre varied considerably in approach. Some studies used whole
foods such as wholegrain cereals and breads and others used fibre isolates which were
commonly provided as a flavoured powder added to water or incorporated into a food vehicle If
high fibre foods were used these were usually substituted with low fibre foods in the control
group. If fibre isolates were used, these were usually substituted instead of a low fibre
supplement. The information on each intervention detailed in table 1 indicates that many of the
studies were balanced in terms of energy and macronutrients for each group.[43]
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Quality of trials
The results of the quality check s are reported in table 2. No studies were excluded from the
review based on the quality check although a sensitivity analysis was carried out on the trials
which were reported to be double blind for all fibre types only and provided as supplemental
data. The quality of the trials was generally good. Unlike many trials involving dietary
manipulation many of the trials stated that they were either single or double blind. Thirteen of
the trials reported participant blinding and eleven trials reported researcher blinding. The
remaining trials either did not provide enough information or stated that there was no blinding.
Blinding was possible due to the fact that fibre supplements can be given as a drink, with the
vehicle being similar in appearance and flavour provided to the control group. Quality was
poor in other areas of assessment, particularly in terms of reporting. In many trials allocation
sequence generation and allocation concealment were not adequately reported.
All fibre types
Results included in the meta-analysis were obtained from seven out of the twelve possible
groups of fibre namely, arabinoxylan rich diets (high in wholegrain foods), beta-glucan rich
diets (high in oat and barley fibre), chitosans, mannans, pectins, xylans and alginates. There
were no trials included in the review that assessed the effects of interventions containing pectin-
rich foods, glucans, resistant starch, dextrins or fructans.
The difference in daily fibre intake for all fibre types between control and intervention groups
ranged from zero to 30g with a median difference in intake between groups of 6g for all studies.
The overall pooled results for SBP (figure 2) and DBP (figure 3) respectively for all trials,
regardless of fibre type were -0.9 mmHg (95% CI -2.5 to 0.6 mmHg, p=0.25) and -0.7 mmHg
(95% CI -1.9 to 0.5 mmHg, p=0.24) indicating that high fibre diets overall do not significantly
reduce SBP or DBP Heterogeneity was moderate at 43% (p=0.02) and 58% (p<0.01)
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respectively. The funnel plots (see figure 1 and 2, Supplementary Digital Content) indicated
little evidence of small study bias.
A number of factors were explored using meta-regression to determine whether an important
amount of heterogeneity was due to any specific characteristics of the trials (see table 3).
Baseline characteristics of participants, had no impact on heterogeneity, however dose of total
fibre was statistically significant. Each daily gram of fibre reduced SBP by 0.20 mmHg (95%
CI -0.39 to -0.02 mmHg, p=0.03) and DBP by 0.12 mmHg (95% CI -0.19 to -0.06 mmHg,
p<0.01). Trials categorised by low (0-3 g), medium (4-9 g) and high (10 or more grams) fibre
level are shown in figure 4 (SBP) and figure 5 (DBP) where a slight trend from top right to
bottom left can be identified.
The sensitivity analysis of double blind trials included eleven out of eighteen trials. The pooled
results for SBP (see figure 3, Supplemental Digital Content) and DBP (see figure 4,
Supplemental Digital Content) were -0.8 mmHg (95% CI -2.9 to 1.2 mmHg, p=0.43) and -0.5
mmHg (95% CI -2.1 to 1.0 mmHg, p=0.49) respectively providing similar but attenuated results
compared to the overall pooled estimate for all studies. Heterogeneity was higher when
compared with all studies at 60% (p<0.01) and 72% (p<0.01) respectively. Only mannans
maintained a minimum of three trials where all trials in the original analysis remained in the
sensitivity analysis.
Alginates
One trial reported the effect of a diet supplemented with alginates and therefore there were
insufficient data available to obtain a pooled estimate. Jenson et al. conducted a double blind
trial in obese participants, who received either a drink supplemented with an alginate gel
extracted from seaweed or a control drink in conjunction with a hypo-energetic diet. The
authors reported attenuated reductions in blood pressure in the intervention group despite
reporting higher weight loss in the intervention group.
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Arabinoxylan rich
Data were extracted from three RCTs reporting information on blood pressure in relation to
diets higher in dietary fibre from wholegrain food sources. Andersson et al. [44] explored blood
pressure differences in men and women consuming their usual diet with whole grain foods
(Bread, crisp bread, muesli & pasta - minimum 50% wholegrain in provided foods = 112g
wholegrain/day) or with refined grain foods (Bread, crisp bread, muesli & pasta). There was a
marked difference in fibre content between the diets, and body weight increased in both groups
possibly due to the test foods supplementing rather than substituting for usual foods. Olenzki et
al.[45] compared 3 hypoenergetic diets (high fibre, high fibre/low saturated fat and low fat).
Body weight decreased in all 3 diet groups. Kristensen et al.[33] similarly used a hypoenergetic
diet comparing a diet rich in wholewheat products with a diet high in refined wheat foods. None
of the studies reported evidence of an effect of a diet high in wholegrain foods on either systolic
or diastolic blood pressure. The pooled estimates for SBP and DBP respectively were -.1 mmHg
(95% CI -4.6 to 4.4 mmHg, p=0.97) and -0.7 mmHg (95% CI -3.7 to 2.2 mmHg, p=0.63)
indicating that wholegrain foods had no significant effect on blood pressure. Heterogeneity was
low for both SBP (0%, p=0.98) and DBP (0%, p=0.66). A meta-regression did not indicate a
significant dose response (table 3)
Beta-glucan rich
Data were extracted from five RCTs reporting on trials of supplementing diets with beta-glucans
derived from oats.[27, 43, 46-48] The trials studied the effects of whole oats, oat bran-
supplemented foods or oat-based breakfast cereals compared with similar wheat-based test
foods.
Maki et al. compared a high oat beta-glucan diet from oatmeal, ready-to-eat cereal with oat bran
and a powdered form of oat beta-glucan, which provided 8g beta-glucan per day with a control
diet (wheat-based cereal, maltodextrin powder and a low fibre hot cereal, providing 0g beta-
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glucan per day).[43] Saltzman et al. compared wheat-based breakfast cereal with oat-based
cereal.[46], He and Davy compared wheat with oats and/oat bran[27, 47] and Charlton [48]
compared a bowl of oat porridge and oat cereal bars with puffed rice and wheat bars.
The pooled estimates for beta-glucans and SBP and DBP respectively were -2.7 mmHg (95%
CI, -4.7 to -0.7 mmHg) and -1.5 mmHg (95% CI, -2.7 to -0.2 mmHg) indicating that
consumption of a high beta-glucan diets significantly reduces blood pressure. These results were
significantly different from zero for both SBP (p<0.01) and DBP (p=0.02). Heterogeneity
denoted by I2 was low for SBP (0%, p=0.65) and DBP (0%, p=0.89). A meta-regression did not
indicate a significant dose response (table 3).
Chitosan
Data were extracted from one trial with four arms which assessed the impact of 1.2 g of
microcrystalline chitosan (a product of chitin) on blood pressure and lipids of carriers and non-
carriers of the Apolipoprotein E 4 gene. Carriers were reported to have slightly higher SBP and
DBP on the higher fibre diet whereas non-carriers were reported as having a slightly lower BP
on the higher fibre diet. The limited evidence from one trial indicated that there was not enough
conclusive evidence to determine whether or not there is an association between blood pressure
and chitosan consumption.
Mannans
Data were extracted from four trials supplementing diets with mannans which include different
soluble fibres.[28, 30, 49, 50] Landin et al [28] supplemented the participant’s normal daily diet
with 3 daily drinks, each containing 10 g of guar gum and compared this with drinks containing
granulated gelling starch. Wood et al. [30] supplemented a hypo-energetic, low carbohydrate
diet with 6 capsules containing a total of 3 g of Konjac-mannan, a viscous soluble fibre that is a
constituent of Konjac root. Grube et al. [49] supplemented the diet with 3 g of a fibre complex
derived from Opuntia ficus-indica and enriched with soluble fibre or a placebo consisting of
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cellulose. Reimer et al. [50] supplemented the diet with 15 g of a complex fibre powder or
placebo mixed with yoghurt All four studies were double blind.
The pooled estimates for mannans and SBP and DBP respectively were 0.4 mmHg (95% CI, -
4.3 to 5.0 mmHg) and 1.7 mmHg (95% CI, -4.3 to7.6 mmHg) indicating that consumption of a
diet high in mannans has no significant effect on SBP or DBP . This estimate was not
significantly different from zero for SBP (p=0.88) or DBP (p=0.58). Heterogeneity denoted by
I2 was high at 81% for SBP (p<0.01) and 91% for DBP (p<0.01). A meta-regression did not
indicate a significant dose response (table 3).
Pectins
Data were extracted from two trials supplementing diets with pectins, soluble fibres originating
from the cell walls of plants. In the study conducted by Bell et al.[26], the intervention was
given to participants in the form of a fibre enriched cereal. Participants were randomised to
receive pectin-enriched cereal (11% soluble fibre) or a placebo (cornflakes). Cereals were
administered as 57g portions and were consumed as part of breakfast. There was no difference
in total fibre consumed between the intervention and control groups and blood pressure reduced
in all groups. In the study by Schwab [51], participants with impaired glucose metabolism were
provided with two drinks enriched with a daily total of 16g of sugar beet pectin or polydextrose
control. Systolic and diastolic blood pressure decreased to a larger degree in the intervention
group. As there were fewer than three trials a pooled estimate was not generated.
Xylans
Data were extracted from three RCTs reporting results of interventions involving xylans,
insoluble and soluble fibres originating from the cell walls of plants [25, 26, 31]. These were
administered in the form of fibre ‘tablets’ containing vegetable, citrus and cereal-derived
fibre[31] or psyllium [25] or as a psyllium enriched cereal.[26] Birketvedt et al reported that the
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high fibre diet participants had a lower SBP and DBP but the remaining two trials reported no
difference in blood pressure.
The pooled estimates for xylans and SBP and DBP were -1.4 mmHg (95% CI, -5.5 to 2.8
mmHg) and -0.8 mmHg (95% CI, -3.9 to2.3 mmHg indicating that consumption of a diet high in
xylans has no significant effect on blood pressure. These estimates were not significantly
different from zero for SBP (p=0.52) or DBP (p=0.61). Heterogeneity denoted by I2 was
moderate at 51% for SBP (p=0.37) and 45% for DBP (p=0.16). A meta-regression did not
identify a significant dose response (table 3).
Discussion
Summary of results
The results from this systematic review provide little evidence that an increase of total fibre
intake has an impact on blood pressure. H, however, higher doses of individual fibre types, in
particular beta-glucans, significantly reduce systolic and diastolic blood pressure in healthy
individuals. Higher total fibre was significantly associated with lower blood pressure with each
1g increase in total fibre associated with 0.2 mmHg reduction in SBP and 0.12 mmHg reduction
in DBP, however but this was largely driven by one study by Landin[28] et al which reported
dramatic substantial reductions in blood pressure with a very high doses (of 30g) of fibre.
Notably, tThe association between fibre dose and blood pressure was not significant when this
study was excluded (data not shown).
In general, the studies included in the review reported reductions in systolic and diastolic blood
pressure in both groups but larger reductions were reported from participants with a higher beta-
glucan intake. Systolic and diastolic blood pressure were 2.7 and 1.5 mmHg lower respectively
in the higher beta-glucan group. Weight loss was 0.5kg higher, on average, for participants
taking beta-glucans in the three studies where weight was reported and therefore some of the
reduction in blood pressure may, be partly, be due to weight loss. IHowever it is unlikely, 15
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however, that the improvements in blood pressure can be completely explained by weight loss
as studies involving alternative types of fibre did not result in similar benefits in blood pressure.
For the trials reporting significant blood pressure reduction due to beta-glucans, the supplement
dose provided to participants in the intervention varied from 4 g to 15 g, however, in studies
with a larger supplement, participants reduced intake of fibre from other sources and therefore
differences in soluble fibre over the whole day varied only from 4 to 7 g for studies where this
was reported. There was no evidence that the difference in the dose of beta-glucans was
important although the actual difference was not reported in all studies.
Mechanisms
The mechanisms for the effect of high beta-glucans and blood pressure are not clear. Beta-
glucans are viscous soluble polysaccharides that occur in the endosperm cell walls of grains.
They are composed of glucose molecules with mixed β-(1→4) and β-(1→3) bonds and oats and
barley are recognised as particularly rich sources. Considerable variation in the amount of beta-
glucans in oats and oat products exists which is due to varietal and processing influences.
Commercial rolled oats may contain in the region of 3 to 5% beta-glucan and oat bran between 6
to 10%.[52]. It has been suggested that viscous soluble fibres lower blood pressure due to effects
on peripheral insulin sensitivity although this is controversial[43] Various methods have shown
that higher levels of fermentable fibre in the gut are associated with improved insulin sensitivity.
[53]
It is also possible that high intakes of beta-glucans help promote weight loss and reduce blood
pressure compared to other fibre types.
Comparison with previous studies and reviews
The results from this review have some similarities with previous reviews of trials [13] [14] and
prospective studies of blood pressure and incident hypertension.[54] More detailed information
is obtained here on the effect of different types of fibre on blood pressure not previously
16
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348
349
350
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353
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366
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reported. Streppel et al. concluded that there was some support for a larger effect of soluble
fibre on BP but did not quantify this effect and treated different types of soluble fibre altogether
in one group.[14] If beta-glucan was the most common type of soluble fibre this could have
driven the results.
Such changes in blood pressure seen here are clinically important. For example, a reduction in
diastolic blood pressure of 5 mmHg is associated with a reduction in stroke of 34% and
coronary heart disease of 21% respectively.[55] Importantly, the reduction in systolic blood
pressure of nearly 3 mmHg seen with beta-glucan rich diets is very similar to the effect of a low
salt diet in a non-hypertensive population as reported in a large review by He et al.[56] Diets
high in beta-glucans may have the potential to reduce blood pressure comparable to a sizeable
decrease in salt intake and consequently reduce CVD risk by approximately 10%.[56] Beta-
glucans also reduce LDL cholesterol - further reducing cardiovascular risk. Yet evidence from
systematic reviews of prospective studies suggests that high total fibre consumption reduces risk
of CVD.[57]
Previous research has tended to group together all soluble fibres when assessing effects on risk
markers of CVD. We found that an increase in daily intake of more than 10 g was needed in
order to see a benefit in BP for some of these other fibre types such as xylans, pectins and
mannans although there were not enough studies to formally test this hypothesis for each fibre
type. This may be because some of the studies were designed to assess the impact of dietary
fibre tablets (using quite small doses of fibre) compared to placebo tablets and the dose may
have been insufficient to detect any benefits on blood pressure over and above any differences
due to weight loss if participants were on a weight loss diet.
Although the aim of the review was to include healthy participants many of the studies included
participants who had higher than average body weight or lipid profile. It is probable that
younger healthy individuals will have an attenuated response to dietary factors such as fibre as
17
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was seen in a previous review of fibre and blood pressure[13] as well as in a review of dietary
salt and blood pressure.[58]
Strengths of this review
This is the first systematic review that reports on the effect of different types of fibre
distinguished by their chemical structure on blood pressure in non-diseased populations. It
included only RCTs, of at least 6 weeks in duration. More than half of the trials included in this
analysis were double blind trials and therefore of high quality. Traditionally, fibre types are
categorised as soluble or insoluble however many types of fibre contain a mixture of both and
therefore our categorisation based on chemical structure is a strength of this review. Finally, the
pooling of data enabled the detection of clinically meaningful differences in blood pressure. The
numbers needed to detect a 5 mmHg difference with sufficient power are estimated to be
between 60 and 70 participants.[59]
Limitations
The evidence presented here is most consistent and most convincing for beta-glucans where
there were sufficient trials included. There are also enough data to provide evidence for
additional fibre types including arabinoxylan rich, xylans and mannans. However there was a
lack of data to enable us to come to any conclusions about alginates, chitosan or pectins or the
five fibre types where no data were available. There may be other methods of categorising fibre
type based on rheology and molecular weight that are also important in driving change in
metabolic risk that we did not look at in this review.
Most of the studies in this review included predominantly overweight or obese participants and
the primary aim of many of the studies was weight loss. As many markers of CVD, including
blood pressure, are related to weight and weight loss, it was difficult to isolate the contribution
of the diet, independently from changes in weight. However, in many of the studies weight loss
was similar in both groups and therefore the difference between groups was relatively small.
18
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399
400
401
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405
406
407
408
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411
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417
418
19
Although the aim of RCTs is to independently assess the contribution of fibre type on blood
pressure it is possible that other aspects of the diet were changed in addition to fibre that could
have had an impact on blood pressure. Information provided from individual studies indicated
that most studies made a reasonable attempts to maintain the macro-nutrient content of the diet.
In addition, some of the studies were double blind and used a fibre supplement which made it
less likely that other aspects of the diet could have been altered to a great extent. Additional
plant sources of fibre such as fruit, vegetables and legumes which contain large amounts of
active compounds including protein, were excluded from the analysis in order to isolate fibre.
Although included in the search strategy, the review did not include any results from children
and included only one trial recruiting adolescents and therefore the results from this review
cannot be extrapolated to younger age groups. This was part of a larger review and, therefore,
some studies were excluded that which only reported results in figures were excluded, and
without we did not contacting authors due to time constraintsfor their data.
Further recommendations
Many countries include recommended levels of total fibre as part of nutrition policy but specific
types of fibre are rarely mentioned. In the UK 18 g of NSP daily are recommended.[60] A third
of this could come from beta-glucan rich food. Beta-glucans were provided to participants in
the form of cereal (both hot and cold) as well as baked goods such as bread, muffins, biscuits
and cereal bars. An increase in the region of 5 g of beta-glucans could be achieved with a daily
bowl of porridge or oat bran cereal together with an enriched snack such as a cereal bar. The
results from this review together with the results from previous reviews on fibre and blood
lipids[61] provide strong evidence of the multiple health benefits of beta-glucans. Blood
pressure and blood lipids are both important markers of CVD and therefore encouraging a
higher intake of beta-glucan rich food has the potential to improve the risk factors for heart
disease and stroke.
19
419
420
421
422
423
424
425
426
427
428
429
430
431
432
433
434
435
436
437
438
439
440
441
442
443
20
More research is needed in normal weight, healthy individuals which may necessitate larger
sample sizes and longer follow up times to improve power.
Conclusion
Beta-glucan rich foods containing oats appear to be particularly beneficial in terms of reducing
systolic and diastolic blood pressure. There was limited evidence that other fibre types also have
a beneficial effect on blood pressure even when consumed in large amounts.
20
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445
446
447
448
449
21
Acknowledgments
The authors thank Iris Gordon (information specialist) for developing the search strategy and
James Thomas for his work developing the database into which all articles were extracted.
21
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451
452
22
References
1. Collins GS, Altman DG. Predicting the 10 year risk of cardiovascular disease in the United Kingdom: independent and external validation of an updated version of QRISK2. BMJ. 2012; 344:e4181.
2. Lewington S, Clarke R, Qizilbash N, Peto R, Collins R, Prospective Studies C. Age-specific relevance of usual blood pressure to vascular mortality: a meta-analysis of individual data for one million adults in 61 prospective studies. Lancet. 2002; 360 (9349):1903-13.
3. Whelton PK. Epidemiology of hypertension. Lancet. 1994; 344 (8915):101-6.
4. Lim SS, Vos T, Flaxman AD, Danaei G, Shibuya K, Adair-Rohani H, et al. A comparative risk assessment of burden of disease and injury attributable to 67 risk factors and risk factor clusters in 21 regions: a systematic analysis for the Global Burden of Disease Study 2010. The Lancet. 2012; 380 (9859):2224-60.
5. Kearney PM, Whelton M, Reynolds K, Muntner P, Whelton PK, He J. Global burden of hypertension: analysis of worldwide data. Lancet. 2005; 365 (9455):217-23.
6. Department of Health. Health Survey for England; 2011.
7. James PA, Oparil S, Carter BL, Cushman WC, Dennison-Himmelfarb C, Handler J, et al. 2014 evidence-based guideline for the management of high blood pressure in adults: report from the panel members appointed to the Eighth Joint National Committee (JNC 8). JAMA : the journal of the American Medical Association. 2014; 311 (5):507-20.
8. National Institute for Health and Care Excellence. Hypertension: Clinical management of primary hypertension in adults. Clinical guidelines CG127; 2011.
9. Blood Pressure UK. Healthy blood pressure diet. 2008 [cited; Available from: http://www.bloodpressureuk.org/BloodPressureandyou/Yourlifestyle/Eatingwell
10. Neter JE, Stam BE, Kok FJ, Grobbee DE, Geleijnse JM. Influence of Weight Reduction on Blood Pressure: A Meta-Analysis of Randomized Controlled Trials. Hypertension. 2003; 42 (5):878-84.
11. Klag MJ, Whelton PK, Appel LJ. Effect of age on the efficacy of blood pressure treatment strategies. Hypertension. 1990; 16 (6):700-5.
12. British Heart Foundation. Coronary Heart Disease Statistics A Compendium of Health Statistics; 2012.
13. Whelton SP, Hyre AD, Pedersen B, Yi Y, Whelton PK, He J. Effect of dietary fiber intake on blood pressure: a meta-analysis of randomized, controlled clinical trials. Journal of Hypertension. 2005; 23 (3):475-81.
14. Streppel MT, Arends LR, van 't Veer P, Grobbee DE, Geleijnse JM. Dietary Fiber and Blood Pressure: A Meta-analysis of Randomized Placebo-Controlled Trials. Arch Intern Med. 2005; 165 (2):150-6.
15. Wolever TMS, Jenkins DJ, Vuksan V, Jenkins AL, Wong GS, Josse RG. Beneficial Effect of Low-Glycemic Index Diet in Overweight NIDDM Subjects. Diabetes Care. 1992; 15 (4):562-4.
22
453
454455456
457458459460
461
462463464465
466467
468
469470471472473
474475
476477
478479480
481482
483484
485486487
488489490
491492493
23
16. Jenkins DJ, Kendall CW, Augustin LS, Franceschi S, Hamidi M, Marchie A, et al. Glycemic index: overview of implications in health and disease. Am J Clin Nutr. 2002; 76 (1):266S-73S.
17. Livesey G, Taylor R, Hulshof T, Howlett J. Glycemic response and health—a systematic review and meta-analysis: relations between dietary glycemic properties and health outcomes. The American Journal of Clinical Nutrition. 2008; 87 (1):258S-68S.
18. Wanders AJ, van den Borne JJ, de Graaf C, Hulshof T, Jonathan MC, Kristensen M, et al. Effects of dietary fibre on subjective appetite, energy intake and body weight: a systematic review of randomized controlled trials. Obes Rev. 2011; 12 (9):724-39.
19. Liberati A, Altman DG, Tetzlaff J, Mulrow C, Gøtzsche PC, Ioannidis JPA, et al. The PRISMA Statement for Reporting Systematic Reviews and Meta-Analyses of Studies That Evaluate Health Care Interventions: Explanation and Elaboration. Annals of Internal Medicine. 2009; 151 (4):W-65-W-94.
20. Haynes RB, Wilczynski NL. Optimal search strategies for retrieving scientifically strong studies of diagnosis from Medline: analytical survey. BMJ. 2004; 328 (7447):1040.
21. SACN. Scientific consultation: draft SACN Carbohydrates and Health report - June 2014; 2014.
22. Higgins JPT, Altman DG, Gøtzsche PC, Jüni P, Moher D, Oxman AD, et al. The Cochrane Collaboration’s tool for assessing risk of bias in randomised trials. BMJ. 2011; 343.
23. Egger M, Davey Smith G, Altman DG, editors. Systematic Reviews in Healthcare: Meta-analysis in context. 2nd ed: BMJ Books; 2008.
24. Higgins JPT, Thompson SG. Quantifying heterogeneity in a meta-analysis. Statistics in Medicine. 2002; 21 (11):1539-58.
25. de Bock M, Derraik JG, Brennan CM, Biggs JB, Smith GC, Cameron-Smith D, et al. Psyllium supplementation in adolescents improves fat distribution & lipid profile: a randomized, participant-blinded, placebo-controlled, crossover trial. PLoS One. 2012; 7 (7):e41735.
26. Bell LP, Hectorn KJ, Reynolds H, Hunninghake DB. Cholesterol-lowering effects of soluble-fiber cereals as part of a prudent diet for patients with mild to moderate hypercholesterolemia. Am J Clin Nutr. 1990; 52 (6):1020-6.
27. Davy BM, Melby CL, Beske SD, Ho RC, Davrath LR, Davy KP. Oat consumption does not affect resting casual and ambulatory 24-h arterial blood pressure in men with high-normal blood pressure to stage I hypertension. J Nutr. 2002; 132 (3):394-8.
28. Landin K, Holm G, Tengborn L, Smith U. Guar gum improves insulin sensitivity, blood lipids, blood pressure, and fibrinolysis in healthy men. Am J Clin Nutr. 1992; 56 (6):1061-5.
29. Sciarrone SE, Strahan MT, Beilin LJ, Burke V, Rogers P, Rouse IR. Ambulatory blood pressure and heart rate responses to vegetarian meals. J Hypertens. 1993; 11 (3):277-85.
30. Wood RJ, Fernandez ML, Sharman MJ, Silvestre R, Greene CM, Zern TL, et al. Effects of a carbohydrate-restricted diet with and without supplemental soluble fiber on
23
494495496
497498499500
501502503504
505506507508
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525526527
528529530
531532533
534535536
537538
24
plasma low-density lipoprotein cholesterol and other clinical markers of cardiovascular risk. Metabolism: clinical and experimental. 2007; 56 (1):58-67.
31. Birketvedt GS, Aaseth J, Florholmen JR, Ryttig K. Long-term effect of fibre supplement and reduced energy intake on body weight and blood lipids in overweight subjects. Acta medica. 2000; 43 (4):129-32.
32. Pasman WJ, Westerterp-Plantenga MS, Muls E, Vansant G, van Ree J, Saris WH. The effectiveness of long-term fibre supplementation on weight maintenance in weight-reduced women. Int J Obes Relat Metab Disord. 1997; 21 (7):548-55.
33. Kristensen M, Toubro S, Jensen MG, Ross AB, Riboldi G, Petronio M, et al. Whole grain compared with refined wheat decreases the percentage of body fat following a 12-week, energy-restricted dietary intervention in postmenopausal women. J Nutr. 2012; 142 (4):710-6.
34. Pasman WJ, Westerterp-Plantenga MS, Saris WH. The effectiveness of long-term supplementation of carbohydrate, chromium, fibre and caffeine on weight maintenance. Int J Obes Relat Metab Disord. 1997; 21 (12):1143-51.
35. Marett R, Slavin JL. No long-term benefits of supplementation with arabinogalactan on serum lipids and glucose. J Am Diet Assoc. 2004; 104 (4):636-9.
36. Rigaud D, Ryttig KR, Angel LA, Apfelbaum M. Overweight treated with energy restriction and a dietary fibre supplement: a 6-month randomized, double-blind, placebo-controlled trial. Int J Obes. 1990; 14 (9):763-9.
37. Swain JF, Rouse IL, Curley CB, Sacks FM. Comparison of the effects of oat bran and low-fiber wheat on serum lipoprotein levels and blood pressure. The New England journal of medicine. 1990; 322 (3):147-52.
38. Niv E, Shapira Y, Akiva I, Rokhkind E, Naor E, Arbiv M, et al. Effect of levan supplement in orange juice on weight, gastrointestinal symptoms and metabolic profile of healthy subjects: results of an 8-week clinical trial. Nutrients. 2012; 4 (7):638-47.
39. Salinardi TC, Rubin KH, Black RM, St-Onge MP. Coffee mannooligosaccharides, consumed as part of a free-living, weight-maintaining diet, increase the proportional reduction in body volume in overweight men. J Nutr. 2010; 140 (11):1943-8.
40. Cairella G, Cairella M, Marchini G. Effect of dietary fibre on weight correction after modified fasting. Eur J Clin Nutr. 1995; 49 Suppl 3:S325-7.
41. Smith KN, Queenan KM, Thomas W, Fulcher RG, Slavin JL. Physiological effects of concentrated barley beta-glucan in mildly hypercholesterolemic adults. J Am Coll Nutr. 2008; 27 (3):434-40.
42. Pal S, Khossousi A, Binns C, Dhaliwal S, Radavelli-Bagatini S. The effects of 12-week psyllium fibre supplementation or healthy diet on blood pressure and arterial stiffness in overweight and obese individuals. Br J Nutr. 2012; 107 (5):725-34.
43. Maki KC, Galant R, Samuel P, Tesser J, Witchger MS, Ribaya-Mercado JD, et al. Effects of consuming foods containing oat beta-glucan on blood pressure, carbohydrate metabolism and biomarkers of oxidative stress in men and women with elevated blood pressure. Eur J Clin Nutr. 2007; 61 (6):786-95.
44. Andersson A, Tengblad S, Karlstrom B, Kamal-Eldin A, Landberg R, Basu S, et al. Whole-grain foods do not affect insulin sensitivity or markers of lipid peroxidation
24
539540
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569570
571572573
574575576
577578579580
581582
25
and inflammation in healthy, moderately overweight subjects. J Nutr. 2007; 137 (6):1401-7.
45. Olendzki BC, Ma Y, Schneider KL, Merriam P, Culver AL, Ockene IS, et al. A simple dietary message to improve dietary quality: Results from a pilot investigation. Nutrition. 2009; 25 (7-8):736-44.
46. Saltzman E, Das SK, Lichtenstein AH, Dallal GE, Corrales A, Schaefer EJ, et al. An oat-containing hypocaloric diet reduces systolic blood pressure and improves lipid profile beyond effects of weight loss in men and women. J Nutr. 2001; 131 (5):1465-70.
47. He J, Streiffer RH, Muntner P, Krousel-Wood MA, Whelton PK. Effect of dietary fiber intake on blood pressure: a randomized, double-blind, placebo-controlled trial. J Hypertens. 2004; 22 (1):73-80.
48. Charlton KE, Tapsell LC, Batterham MJ, O'Shea J, Thorne R, Beck E, et al. Effect of 6 weeks' consumption of beta-glucan-rich oat products on cholesterol levels in mildly hypercholesterolaemic overweight adults. Br J Nutr. 2012; 107 (7):1037-47.
49. Grube B, Chong PW, Lau KZ, Orzechowski HD. A natural fiber complex reduces body weight in the overweight and obese: a double-blind, randomized, placebo-controlled study. Obesity (Silver Spring). 2013; 21 (1):58-64.
50. Reimer RA, Yamaguchi H, Eller LK, Lyon MR, Gahler RJ, Kacinik V, et al. Changes in visceral adiposity and serum cholesterol with a novel viscous polysaccharide in Japanese adults with abdominal obesity. Canadian journal of diabetes. 2013; 37 Suppl 2:S246.
51. Schwab U, Louheranta A, Torronen A, Uusitupa M. Impact of sugar beet pectin and polydextrose on fasting and postprandial glycemia and fasting concentrations of serum total and lipoprotein lipids in middle-aged subjects with abnormal glucose metabolism. Eur J Clin Nutr. 2006; 60 (9):1073-80.
52. Wursch P, Pi-Sunyer FX. The role of viscous soluble fiber in the metabolic control of diabetes. A review with special emphasis on cereals rich in beta-glucan. Diabetes Care. 1997; 20 (11):1774-80.
53. Chu Y. Oats Nutrition and Technology: Wiley-Blackwell; 2013.
54. He J, Whelton PK. Effect of Dietary Fiber and Protein Intake on Blood Pressure: A Review of Epidemiologic Evidence. Clinical and Experimental Hypertension. 1999; 21 (5-6):785-96.
55. MacMahon S, Peto R, Cutler J, Collins R, Sorlie P, Neaton J, et al. Blood pressure, stroke, and coronary heart disease. Part 1, Prolonged differences in blood pressure: prospective observational studies corrected for the regression dilution bias. Lancet. 1990; 335 (8692):765-74.
56. He FJ, MacGregor GA. Salt, blood pressure and cardiovascular disease. Curr Opin Cardiol. 2007; 22 (4):298-305.
57. Threapleton DE, Greenwood DC, Evans CE, Cleghorn CL, Nykjaer C, Woodhead C, et al. Dietary fibre intake and risk of cardiovascular disease: systematic review and meta-analysis. BMJ. 2013; 347:f6879.
58. He FJ, MacGregor GA. Effect of modest salt reduction on blood pressure: a meta-analysis of randomized trials. Implications for public health. J Hum Hypertens. 2002; 16 (11):761-70.
25
583584
585586587
588589590
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604605606607
608609610
611
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615616617618
619620
621622623
624625626
26
59. Uen S, Fimmers R, Brieger M, Nickenig G, Mengden T. Reproducibility of wrist home blood pressure measurement with position sensor and automatic data storage. BMC cardiovascular disorders. 2009; 9:20.
60. Department of Health. Dietary Reference Values for Food Energy and Nutrients for the United Kingdom: HMSO; 1991.
61. Brown L, Rosner B, Willett WW, Sacks FM. Cholesterol-lowering effects of dietary fiber: a meta-analysis. The American Journal of Clinical Nutrition. 1999; 69 (1):30-42.
62. Georg Jensen M, Kristensen M, Astrup A. Effect of alginate supplementation on weight loss in obese subjects completing a 12-wk energy-restricted diet: a randomized controlled trial. Am J Clin Nutr. 2012; 96 (1):5-13.
63. Lehtimaki T, Metso S, Ylitalo R, Rontu R, Nikkila M, Wuolijoki E, et al. Microcrystalline chitosan is ineffective to decrease plasma lipids in both apolipoprotein E epsilon 4 carriers and non-carriers: a long-term placebo-controlled trial in hypercholesterolaemic volunteers. Basic & clinical pharmacology & toxicology. 2005; 97 (2):98-103.
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Table 1: Trial characteristics
First
Author,
year
Characteristics of
participants
Design &
length of f/u
N of
partici-
pants
Intervention design Diet characteristics
Differenc
e in fibre
(g)
Difference
in weight
loss in kg1
Andersson,
2007[44]
Sweden
27% Male
Mean age: (59)
Mean BMI: (28)
≥ 1 CHD risk factor
Crossover
6 weeks
34 Arabinoxylans
Substitution with wholegrain
foods (Bread, bread, muesli &
pasta) Minimum 50%
wholegrain in provided foods
= 112g wholegrain/day.
Intervention. g/d: C 143 P
28 F 8, Energy: 3180kJ/d,
Fibre g/d:18
Control. g/d: C 145 P 23 F
14, Energy: 3340kJ/d, Fibre
g/d:6
12 Values not
reported
Bell,
1990[26]
USA
100% Male
Age range: 24-59
Body weight >130% of
ideal
Free of chronic disease
Parallel
6 weeks
60 Pectins & Xylans
Substitution with Pectin or
psyllium enriched cereals
compared with cornflakes
50% total soluble fibre in
cereal was from pectin.
Not reported n/a 0.6 (Pectins)
0.1 (Xylans)
Birketvedt,
2000[31]
Norway
100% Female
Mean age: (40)
Double
blind
Parallel
53 Xylans
Supplementation with tablets
containing 6g of grain/citrus
Not reported Values not
reported
27
644
28
First
Author,
year
Characteristics of
participants
Design &
length of f/u
N of
partici-
pants
Intervention design Diet characteristics
Differenc
e in fibre
(g)
Difference
in weight
loss in kg1
Mean BMI: (28) 24 weeks fibre compared with placebo
tablets.
*Cairella,
1995[40]
(Cairella et
al., 1995)
Italy
27% Male
Mean age: (36)
BMI: (37)
Double
blind
Parallel
60 days
30 Xylans
Supplement of citrus fibre
tablets containing 6g of fibre
compared with placebo
Not reported n/a Values not
reported
Charlton.,
2011[48]
Australia
48% male
Mean age: (51)
Mean BMI: (27)
Parallel
6 weeks
90 Beta-glucans
Substitution with oat porridge
and oat based cereal bars (3g
fibre) with puffed rice and
wheat bars as control
Intervention:.%E C 46 P 20
F 29
Control:.%E C 47 P 19 F 31
n/a 0.7
Davy,
2002[27]
USA
100% Male
Mean age: (59)
Mean BMI: (29)
Parallel
12 weeks
36 Beta-glucans
Substitution with 60g oatmeal
and 76g oat bran ready-to-eat
cold cereal (14g/day of fibre,
5.5g/d beta-glucan) compared
Intervention1. g/d: C 112 P
14 F 3, Energy: 2008kJ/d,
Fibre g/d:14
Control:. g/d: C 95 P 21 F 8,
Energy: 2146kJ/d, Fibre
0 0.2
28
29
First
Author,
year
Characteristics of
participants
Design &
length of f/u
N of
partici-
pants
Intervention design Diet characteristics
Differenc
e in fibre
(g)
Difference
in weight
loss in kg1
DBP 85-99mm and/ or
SBP 130-159 mmHg
Fibre <30g/d
with wheat based control. g/d:14
De Bock,
2012[25]
New Zealand
100% male Age:15-16
years
Mean BMI: (26)
Crossover
Participant
blind
6 weeks
45 Xylans
Supplementation with 6g/day
psyllium supplement
compared with 6g/day of
potato starch control.
Not reported n/a Values not
reported
Grube.,
2013[49]
Germany
26% Male
Mean age: (45)
Mean BMI: (29)
Double
blind
Parallel
12 weeks
123 Mannans
Supplementation with two
tablets of IQP fibre
supplement taken 3 times per
day after meals compared
with cellulose tablet placebo.
Not reported n/a -2.5
29
30
First
Author,
year
Characteristics of
participants
Design &
length of f/u
N of
partici-
pants
Intervention design Diet characteristics
Differenc
e in fibre
(g)
Difference
in weight
loss in kg1
He,
2004[47]
USA
40% Male
Mean age: (48)
Mean BMI: (29)
Double
blind
Parallel
12 weeks
110 Beta-glucans
Substitution with 60g oat bran
in a muffin and 84g of
oatmeal squares cereal daily
fibre 7.7g/d compared with
refined wheat and corn
control.
Intervention:. g/d: C 113.3 P
24 F 13.7, Energy 652
kcal/d, Fibre g/d:16
Control: 2. g/d: C 108.4 P
10.8 F 11, Energy 567
kcal/d, Fibre g/d:3
13 0.7
Jensen,
2012[62]
Denmark
33% male
Mean age: (43)
Mean BMI: (34)
Parallel
Double
blind 12
weeks
80 Alginates
Supplementation with
Alginate supplement as a
blackcurrant flavoured
powder mix mixed with water
3 times per day compared
with maltodextrin control.
Intervention:.Energy
1638kcal/d
Control: .Energy 1608kcal/d
n/a 1.2
Kristense
n.,
2011[33]
Denmark
100% female (post-
Parallel 14
weeks
72 Arabinoxylans
Substitution with 105g
wholegrain foods daily
Intervention: Energy 2MJ C
87g/d P 17g/d F 7g/d fibre
6 0.9
30
31
First
Author,
year
Characteristics of
participants
Design &
length of f/u
N of
partici-
pants
Intervention design Diet characteristics
Differenc
e in fibre
(g)
Difference
in weight
loss in kg1
menopausal)
Mean age: (60)
Mean BMI: (30)
compared with low fibre
cereal foods.
11 g/d
Control: Energy 2MJ C 86
g/d P 16g/d F 7g/d Fibre
5g/d
Landin,
1992[28]
Sweden
100% Male
Mean age: (52)
Mean BMI: (25)
Double
blind
Crossover
6 weeks
25 Mannans
Supplementation with 10g
guar given in a glass of water,
3 times a day before meals
compared with starch
placebo.
Intervention:. g/d: C 445 P
14 F 92, Energy 2875 kcal/d
Control: g/d: C 445 P 14 F
92, Energy 2875 kcal/d
n/a Values not
reported
Lehtimaki,
2005[63]
Finland
42% Male
Mean age: (44)
Mean BMI: (26)
Stratified by
apolipoprotein E
Double
blind
Crossover
3 months
130 Chistosan
Supplementation with 1.2 g
chitosan twice daily (total
2.4g/d) compared with starch
capsules.
Not reported n/a 0 (carrier)
0.2 (non
carrier)
31
32
First
Author,
year
Characteristics of
participants
Design &
length of f/u
N of
partici-
pants
Intervention design Diet characteristics
Differenc
e in fibre
(g)
Difference
in weight
loss in kg1
genotype
Maki,
2007[43]
USA
55% Male
Age: >40
BMI: (32) SBP 130-
179mmHg DBP 85-
109mmHg
Fibre <20g/d
Parallel 12
weeks
97 Beta-glucans
Substitution with 90g/d oat
bran cereal + 60g/d oatmeal +
20g/d powdered oat beta-
glucan. 7.7g/d beta-glucan
compared with wheat cereal
and low fibre supplements.
Intervention:. g/d: C 124.3 P
20.3 F 8.9, Energy: 658
kcal/d, Fibre g/d:17
Control: g/d: C 139.5 P 10 F
2.1Energy: 641 kcal/d, Fibre
g/d:2
15 Values not
reported
*Marett,
2004[35]
USA
52% Male
Mean age: (29)
BMI: mean not reported
Double
blind
Parallel 6
months
54 Arabinoxylans
Supplementation with 8.4g/d
Larch or Tamarack
arabinogalactan added to food
or drinks compared with rice
starch placebo.
Not reported n/a Values not
reported
*Niv,
2012[38]
Israel
48% male
Parallel
8 weeks
48 Fructans
Supplementation with 500ml
Orange juice daily containing
Not reported n/a Values not
reported
32
33
First
Author,
year
Characteristics of
participants
Design &
length of f/u
N of
partici-
pants
Intervention design Diet characteristics
Differenc
e in fibre
(g)
Difference
in weight
loss in kg1
Mean age: (36)
Mean BMI: (25)
11.5g Levan fibre compared
with orange juice control.
Olendzki,
2009[45]
USA
16% Male
Mean Age: (48)
Mean BMI: (31)
Parallel
3 months
31 Arabinoxylans
Substitution increasing fibre
to 30g/day compared with
low fibre control. Both diets
low in saturated fat.
Intervention: %E: C 52.1 P
F 26.2, Energy: 1511 kcal/d,
Fibre g/d:24
Control: %E: C 49.9 P F
27.5, Energy: 1523 kcal/d,
Fibre g/d:17
7 -1.4
*Pal,
2012[42]
Australia
51% Male
Age 18-65
BMI 25-40
Participant
blind
Parallel
12 weeks
72 Xylans
Supplementation with fibre
supplement containing 7g of
psyllium mixed with water
and taken 3 times per day
compared with low fibre
control.
Intervention: Energy 7.8MJ,
C 46%, P 19%, F 34%, fibre
40g/d
Control: Energy 8.2MJ, C
45%, P 18%, F 37%, fibre
20g/d
20 Values not
reported
*Pasman, The Netherlands
100% female
Double
blind
39 Mannans Not reported n/a Values not
33
34
First
Author,
year
Characteristics of
participants
Design &
length of f/u
N of
partici-
pants
Intervention design Diet characteristics
Differenc
e in fibre
(g)
Difference
in weight
loss in kg1
1997[32] Mean age: (41)
Mean BMI: (33)
Parallel
14 months
Supplementation with 20g
guar gum in 2x10g doses
daily to be consumed in
afternoon and evening.
Dissolved in 200ml
water/coffee/orange juice
compared with no
supplement..
reported
Reimer,
2013[50]
Japan
44% Male
Age 20-65
Mean BMI: (27)
Double
blind
Parallel
14 weeks
64 Mannans
Supplementation PGX
supplement containing fibre
in 5g packets mixed with
yoghurt taken 3 times per day
compared with placebo
containing rice flour in 5g
packets mixed with yoghurt.
Not reported n/a 0
*Rigaud, France Double 52 Pectins Not reported n/a Values not
34
35
First
Author,
year
Characteristics of
participants
Design &
length of f/u
N of
partici-
pants
Intervention design Diet characteristics
Differenc
e in fibre
(g)
Difference
in weight
loss in kg1
1990[36] 21% Male
Mean age: (37)
Mean BMI: (29)
blind
Parallel
6 months
Supplementation with a
dietary fibre tablets (beet,
barley, citrus fibre, 90%
insoluble) providing 7g/day
compared with placebo tablets
containing 1g fibre/d.
reported
*Salinardi,
2010[39]
USA
36% male
Mean age : (46)
Mean BMI: (30)
Double
blind
Parallel
12 weeks
69 Mannans
Supplementation with
beverage twice daily with
meals containing 4.4g of fibre
per drink compared to
placebo beverage twice daily
with meals containing no
fibre.
Not reported n/a Values not
reported
Saltzman,
2001[46]
USA
49% Male
Mean age: (45)
Parallel
6 weeks
43 Beta-glucans
Substitution with 45g/1000
kcal of rolled oats compared
Intervention: g/d: C 229 P
79 F 67, Energy: 7645kJ/d,
3 Values not
reported
35
36
First
Author,
year
Characteristics of
participants
Design &
length of f/u
N of
partici-
pants
Intervention design Diet characteristics
Differenc
e in fibre
(g)
Difference
in weight
loss in kg1
Mean BMI: (26) to 45g/1000 kcal of wheat
products.
Fibre g/d:16
Control: g/d: C 234 P 82 F
69, Energy: 7833kJ/d, Fibre
g/d:12.5
Schwab,
2006[51]
Finland
44% Male
Mean age: (53)
Mean BMI: (29)
Double
blind
Parallel
12 weeks
70 Pectins
Supplementation with Sugar-
beet pectin, drinks.
400ml/day, containing 16g
pectin, of which 76% soluble
fibre compared to
polydextrose control.
Not reported n/a 0.6
*Sciarrone,
1993[29]
Australia
100% Male
Mean age: (41)
Mean BMI: (26)
Normal BP only
Parallel
6 weeks
21 Arabinoxylan rich
Substitution with 35% total
energy complex
carbohydrates, 20% sugar +
fibre intake of approx
20g/1000kcal compared to
Intervention: g/d: C 339 P
78 F 86, Energy: 2437
kcal/d
Fibre g/d:41
Control: g/d: C 314 P 100 F
114, Energy: 2658 kcal/d,
17 Values not
reported
36
37
First
Author,
year
Characteristics of
participants
Design &
length of f/u
N of
partici-
pants
Intervention design Diet characteristics
Differenc
e in fibre
(g)
Difference
in weight
loss in kg1
25% total energy complex
carbohydrates, 20% sugar +
fibre intake <8g/1000kcal.
Fibre g/d:24
*Smith,
2008[41]
USA
29% Male
Age 22-66y
BMI <30
Double
blind
Parallel
6 weeks
90 B Glucans
Supplementation with 6g high
molecular weight beta-glucan
per day was given as a dietary
supplement powder,
consumed as a beverage with
morning and evening meals
compared to low molecular
weight beta-glucan.
Not reported n/a 0.7
*Swain,
1990[37]
USA
20% Male
Mean age: 30
BMI: not reported
Double
blind
Crossover
6 weeks
24 Beta-glucans
Supplementation with oat
enriched muffins or entrees
containing a total of 100g oat
bran/d compared to low fibre
Intervention: %E: Fat 35,
2429 kcal, fibre 39g/d
Control: %E: Fat 30, 2315
21 -0.1
37
38
First
Author,
year
Characteristics of
participants
Design &
length of f/u
N of
partici-
pants
Intervention design Diet characteristics
Differenc
e in fibre
(g)
Difference
in weight
loss in kg1
wheat based foods. kcal, fibre 18g/d
Wood,
2007[30]
USA
100% Male
Mean age: 39
Mean BMI: 30
SBP <160mmHg DBP
<90mmHg
Double
blind
Parallel
12 weeks
30 Mannans
Supplementation with 3g/d
Konjac-mannan compared to
maltodextrin placebo
supplement.
Intervention: %E: C 12.5 P
28.4 F 60.7, Energy:
6866kJ/d, Fibre g/d:13
Control: %E: C 13.3 P 27.1
F 59.6, Energy: 7017kJ/d,
Fibre g/d:10
3 -0.1
Abbreviations: GI=glycaemic Index
GL=glycaemic load
%E= percent energy
g/d=grams per day
C =carbohydrate
P=protein
F=fat
*Not included in meta-analysis
1Weight loss of control group-weight loss of intervention group (positive value indicates higher weight loss or less weight gain in intervention group)
38
645
646
647
648
649
650
651
652
653
654
39
Table 2: Assessment of bias for trials included in the meta-analysis
First author, year
Allocation
sequence
generatio
n
Allocati
on
conceal
ment
Partici
pant
blindin
g
Resear
cher
Blindin
g
Incompl
ete
outcom
e
reportin
g
Selectiv
e
outcom
e
reportin
g
Any
other
bias
Andersson, 2007 Unclear Unclear Bias Bias No Bias No Bias No Bias
Bell, 1990 Unclear Unclear No
Bias
No
Bias
No Bias No Bias No Bias
Birketvedt, 2000 Unclear Unclear No
Bias
No
Bias
No Bias No Bias No Bias
Charlton, 2012 No bias No bias No
Bias
Bias No bias No bias Unclear
Davy, 2002 Unclear Unclear Bias No
Bias
No Bias No Bias No Bias
39
655
40
First author, year
Allocation
sequence
generatio
n
Allocati
on
conceal
ment
Partici
pant
blindin
g
Resear
cher
Blindin
g
Incompl
ete
outcom
e
reportin
g
Selectiv
e
outcom
e
reportin
g
Any
other
bias
De Bock, 2012 No bias Unclear No
bias
Bias No bias No bias No bias
Grube, 2013 No bias No bias No
bias
No
bias
No bias No bias No bias
He, 2004 Unclear No Bias No
Bias
No
Bias
No Bias No Bias No Bias
Jensen, 2012 No bias No bias No
bias
No
bias
No bias No bias Unclear
Kristensen, 2011 Unclear Unclear Bias Bias No bias No bias Unclear
Landin, 1992 Unclear Unclear No No No Bias No Bias No Bias
40
41
First author, year
Allocation
sequence
generatio
n
Allocati
on
conceal
ment
Partici
pant
blindin
g
Resear
cher
Blindin
g
Incompl
ete
outcom
e
reportin
g
Selectiv
e
outcom
e
reportin
g
Any
other
bias
Bias Bias
Lehtimaki, 2005 No Bias No Bias No
Bias
No
Bias
No Bias No Bias No Bias
Maki, 2007 Unclear Unclear No
Bias
No
Bias
Bias No Bias No Bias
Olendzki, 2009 No Bias Unclear Bias Bias Bias Unclear Unclear
Reimer, 2013 Unclear Unclear No
bias
No
bias
No Bias No bias Unclear
Saltzman, 2001 No Bias Unclear Unclea
r
Unclea
r
Bias No Bias No Bias
41
42
First author, year
Allocation
sequence
generatio
n
Allocati
on
conceal
ment
Partici
pant
blindin
g
Resear
cher
Blindin
g
Incompl
ete
outcom
e
reportin
g
Selectiv
e
outcom
e
reportin
g
Any
other
bias
Schwab, 2006 Unclear Unclear No
Bias
No
Bias
Unclear No Bias No Bias
Wood, 2007 No Bias Unclear No Bias No Bias No Bias No Bias No Bias
42
656
43
Table 3: Meta-regression and subgroup analysis using random effects model indicating
change in blood pressure in mmHg for each higher unit of variable
VariableOutcome No.
studies
Coefficient
(mmHg/unit)*
95% CI
(mmHg/unit)p value
Residual I2 (%)
Mean age at baseline (years) SBP
DBP
17
15
-0.05
-0.05
-.24 to 0 .13
-0.18 to -0.07
0.54
0.38
43
54
BMI at baseline (kg/m2) SBP
DBP
18
16
0.49
0.14
-0.22 to-1.20
-.42 to 0.69
0.17
0.61
39
56
Fibre dose for all fibre types
(g)
SBP
DBP
20
18
-0.20
-0.12
-.39 to -.02
-.19 to -.06
0.03
<0.01
25
20
Fibre dose for beta-glucans (g) SBP
DBP
5
4
0.05
-0.07
-0.76 to 0.86
-0.85 to 0.71
0.85
0.74
0
0
Fibre dose for Arabinoxylan
rich (g)
SBP
DBP
3
3
-0.19
0.23
-12.98 to 12.61
-6.12 to 6.57
0.88
0.73
0
0
Fibre dose for Mannans (g) SBP
DBP
4
3
-0.29
-0.36
-1.13 to 0.55
-1.34 to 0.61
0.28
0.13
74
0
Fibre dose for Xylans (g) SBP
DBP
3
3
-0.57
-0.43
-4.13 to 3.00
-3.34 to 2.47
0.29
0.31
0
0
Baseline difference between
groups (mmHg)
SBP
DBP
15
14
-0.29
0.08
-1.08 to 0.50
-.82 to 0.97
0.44
0.86
29
34
Difference in weight change
between groups (kg)
SBP
DBP
14
12
0.09
-1.65
-1.51 to 1.68
-5.66 to 2.37
0.91
0.38
23
38
43
657
658
659
44
Captions
Figure 1: PRISMA flow chart of included references
Figure 2: Systolic blood pressure and fibre type for all trials
Figure 3: Diastolic blood pressure and fibre type for all trials
Figure 4: Pooled estimates of systolic blood pressure for fibre categorised into low, medium
and high dose
Figure 5: Pooled estimates of diastolic blood pressure for fibre categorised into low, medium
and high dose
Supplemental Digital Content figure 1: Funnel plot for all trials of any fibre type reporting
systolic blood pressure. Estimate is in mmHg.
Supplemental Digital Content figure 2: Funnel plot for all trials of any fibre type reporting
diastolic blood pressure. Estimate is in mmHg.
Supplemental Digital Content figure 3: Pooled estimates of systolic blood pressure for double
blind fibre trials only
Supplemental Digital Content figure 4: Pooled estimates of diastolic blood pressure for
double blind fibre trials only
44
660
661
662
663
664
665
666
667
668
669
670
671
672
673
674
675
676
677
45
Contributors
VJB was the project lead for the main systematic review concerning dietary carbohydrates
and cardio-metabolic health. VJB, DET, CLC searched databases. CPG helped develop
search strategies. Article screening was undertaken by VJB, DET, CLC, CELE and CN. Data
extraction was carried out by VJB, DET, DCG, CLC, CELE and CN. Quality of data
extraction and checking was carried out by DET, CN, CLC and CEW. Statistical analysis was
undertaken by CELE and overseen by DCG. CELE wrote the first draft of the manuscript. All
authors reviewed the manuscript and contributed to manuscript revisions.
45
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679
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681
682
683
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